The main reason for the fact that the grinding effect of a grinding product decreases and finally disappears altogether is that dust from the ground material blocks the product. In conventional grinding products comprising a paper, plastic or woven layer to which abrasive grit particles are applied using a binding agent, different measures have been taken to slow down the blocking rate. For example, the grit density on the surface of the grinding product has been varied, different types of binding agents have been used, a stearate layer has been spread on the grinding product to provide a dust-repellent surface, and the grinding product has even been perforated such that it has been possible to suck the dust through the grinding machine or grinding block at certain points during the grinding.
These known methods, however, have only a slight effect on the blocking rate. For example, the last-mentioned perforated grinding product has the drawback that since the product as such is impervious to air and since during the grinding the product is situated against the surface to be ground, there is very little space for the air streams that should take the dust away.
One known grinding product with improved conveyance of grinding dust as compared with the above conventional products comprises a relatively thick, randomly needle-punched layer of nylon fibres. The product has an open, elastic structure. Using the product, the grinding pressure is even, and the mutual movement of individual threads during the grinding helps to prevent dust from fastening to the product. The connecting manner, however, makes the grinding surface of the nonwoven product uneven and irregular, and the large thickness makes the product bulky and rigid.
U.S. Pat. No. 4,437,269 shows a grinding product comprising a paper layer, a grinding agent being attached to one side of the product, and a fabric being adhered to the other. The free surface of the fabric is raised to form fibre loops or ends by means of which the grinding product can be detachably attached to a supporting surface provided with means, such as hooks or mushroom-like pins, that grip the loops of the cloth. The raised surface of the cloth makes it possible to attach the grinding product to and detach it from the supporting surface in a very quick and simple manner, the supporting surface forming e.g. part of a grinding tool.
U.S. Pat. No. 3,324,609 teaches a grinding product in which a layer of nonwoven fibres is attached to a cloth of woven fibres. A grinding agent is applied to the free surface of the nonwoven layer. The nonwoven layer is attached to the cloth by means of fibres that extend through the cloth and have lumps--produced by heating--at the ends for attaching the fibres to the cloth.
The above known structure has certain drawbacks. For example, the grinding product of the citation becomes rather rigid partly because the nonwoven layer must be rigid to be able to carry the grinding agent, and partly because of the lumps at the ends of the fibres on the other side of the cloth, molten together to some extent. The grinding product is thus relatively rigid.
In addition, production of a grinding product according to U.S. Pat. No. 3,324,609 is very complicated. A nonwoven layer with an even surface on one side and an uneven surface with projecting fibres on the other side is produced first. Then a loose fabric is produced, and the nonwoven layer is placed on the cloth such that some of the fibres of the layer penetrate through the cloth. Finally, a flame is directed towards the cloth so that the ends of the fibres projecting from the cloth melt, forming lumps. It is also to be noted that the lumps at the ends of the fibres effectively hinder conveyance of air and dust through the cloth.